LTE (Long Term Evolution) defines a scheme based on OFDM (Orthogonal Frequency Division Multiplex) as a radio access technology. LTE (Long Term Evolution) thus enables high-speed wireless packet communication at the downlink peak data rate of at least 100 Mbps and the uplink peak data rate of at least 50 Mbps. Further, 3GPP (3rd Generation Partnership Project), which is an international standardization group, has already started studying an LTE-based mobile communication system, LTE-A (LTE-Advanced), in its efforts to bring about even faster communication.
In using LTE or LTE-A, DRX (Discontinuous Reception) is adopted as a method for implementing a power-saving mode of a mobile station in some cases.
DRX is specifically described here. For a mobile station, a first interval that involves monitoring of a PDCCH (Physical Downlink Data Channel), and a second interval that does not involve the monitoring are set. Note that a PDCCH is an L1 signal, which is a Layer 1 signal, and is used for controlling data transmission and reception. In addition, the first interval and the second interval are set so as to occur cyclically, and a cycle corresponding to, as a unit interval, one pair of the first interval and the second interval is called a “DRX cycle”. This “DRX cycle” is set with respect to each mobile station uniquely thereto, not with respect to each application. The first interval may be called “On Duration” in some cases.
In an interval that does not require monitoring of the PDCCH, the mobile station does not need to perform signal processing such as data reception processing, and is therefore allowed to enter the power-saving mode. In the power-saving mode, the mobile station stops, for example, signal processing in a baseband unit.
The DRX cycle is set, at the start of communication, when a base station notifies the mobile station of DRX parameters and the like. An RRC (Radio Resource Control) signal, which is an L3 signal, is used for this notification. Specifically, the mobile station receives the RRC signal, and sets DRX in accordance with DRX parameters contained in the RRC signal. The DRX parameters include, for example, long DRX-Cycle, drx Start Offset, On Duration Timer, and drx-Inactivity Timer, where:
long DRX-Cycle is a parameter that defines a length of the DRX cycle;
drx Start Offset is a parameter that defines the start of the DRX cycle;
On Duration Timer is a parameter that defines a length of the first interval of the DRX cycle; and
drx-Inactivity Timer is a parameter that defines the timing at which to enter an inactive state, and is reset each time when data transmission or reception is performed during On Duration. When a time period set in this drx-Inactivity Timer parameter is up, the inactive state is entered.
Note that it is allowed to set a DRX cycle that is shorter than the DRX cycle set by long DRX-Cycle. When such a DRX cycle is set, the DRX parameters may include drx Short Cycle Timer and short DRX-Cycle, where: short DRX-Cycle corresponds to long DRX-Cycle; and drx Short Cycle Timer corresponds to On Duration Timer.
Here, it is basically not allowed to enter the inactive state under the condition that time has not yet been up on both of On Duration Timer and drx-Inactivity Timer. That is, under the condition that time has been up on both of On Duration Timer and drx-Inactivity Timer, the mobile station is allowed to enter the power-saving mode.
On the other hand, under the control of the base station, there are multiple mobile stations controlled thereby. The timing at which to enter the inactive state is different by mobile station, and therefore, the base station has a possibility of transmitting or receiving data to or from a mobile station at any time, and has a difficulty in entering the power-saving mode.
With regard to this problem, there is a conventional technology that causes a base station to enter the power-saving mode by causing each controlled mobile station to enter an idle state. Here, an idle state means a state where the mobile station is allowed only to receive broadcast information from the base station.
Patent Document 1: Japanese Laid-open Patent Publication No. 2002-158609
However, the above conventional technology does not allow a base station to enter the power-saving mode when only one of multiple mobile stations controlled thereby is in an idle state, i.e., has been enabled to transmit and receive data to and from the base station. Therefore, the technology is not very effective in saving power.